This invention relates to solid fuel pulverizing and firing systems for fossil fuel furnaces of the type, wherein the fossil fuel furnace and a substantial portion of the solid fuel pulverizing and firing system by means of which solid fuel and air is supplied to the fossil fuel furnace, are operated at a predetermined pressure, and more specifically, to a high efficiency exhauster employable in such solid fuel pulverizing and firing systems for fossil fuel furnaces.
There are three basic types of solid fuel pulverizer firing systems in use today. These are the direct-fired system, the semi-direct fired system, and the bin storage system. The simplest and most commonly used of these three systems, and the one to which the present invention is directed, is the direct-fired system. The nature of this latter system is such that solid fuel, e.g., coal, is fed in a suitable manner along with hot gases to a pulverizer. The solid fuel is simultaneously ground and dried within the pulverizer. The drying of the solid fuel is effected by the hot gases as the latter sweep through the pulverizer. As the hot gases sweep through the pulverizer they are cooled and humidified by means of the evaporation of the moisture contained in the solid fuel. Often, an exhauster is employed for purposes of removing the hot gases and the entrained fine solid fuel particles, i.e., the solid fuel that has been ground within the pulverizer, from the pulverizer. Moreover, this exhauster, when so employed, is located on the discharge side of the pulverizer and is operative to effect the delivery of the mixture of hot gases and entrained fine solid fuel particles to a fossil fuel furnace. The main advantages of the direct-fired system are simplicity, low cost and maximum safety. To this end, the fine solid particles, which can be subject to spontaneous combustion and thus are considered to be potentially hazardous, go directly to the fossil fuel furnace at high velocities, and thus are not given the opportunity to collect and possibly ignite spontaneously. Accordingly, the direct-fired system can be operated at the maximum temperatures that safety will permit.
One prior art form of such a direct-fired solid fuel pulverizer firing system is depicted in U.S. Pat. No. 3,205,843 entitled "Pulverized Coal Firing System", which issued on Sep. 14, 1965 and which was assigned to the same assignee as the present patent application. In accordance with the teachings of U.S. Pat. No. 3,205,843, solid fuel passes through the inlet chute 23 of the pulverizer 26 on to the rotating bowl 32 thereof. The solid fuel thus admitted to the pulverizer 26 is pulverized therewithin by means of the grinding rollers 36 of the pulverizer 26, which are mounted within the pulverizer housing to provide a grinding action between the grinding rollers 36 and the grinding ring provided on the rotating bowl 32 of the pulverizer 26. Air passes up through the pulverizer 26 between the housing thereof and the rim of the rotating bowl 32 and as the air passes the rotating bowl 32, pulverized solid fuel is entrained in this air with the air-pulverized solid fuel mixture passing up into the classifier 40 of the pulverizer 26, which is located in the upper portion of the pulverizer 26. The classifier 40 is effective to separate the coarse solid fuel fractions and return these fractions to the rotating bowl 32 of the pulverizer for regrinding, while the fines retained in the air stream pass through the outlet 42 of the pulverizer 26, which is located at the upper end of the classifier 40. From this outlet 42 of the pulverizer 26, the air-pulverized solid fuel mixture is conveyed to the inlet of the exhauster 46 via conduit 44. The air-pulverized solid fuel mixture in mm is conveyed from the exhauster 46 to the fossil fuel furnace 10 through the ducts 48.
Another prior art form of such a direct-fired solid fuel pulverizer firing system is depicted in U.S. Pat. No. 4,552,076 entitled "Coal Fired Furnace Light-Off and Stabilization Using Microfine Pulverized Coal", which issued on Nov. 12, 1985 and which is assigned to the same assignee as the present patent application. In accordance with the teachings of U.S. Pat. No. 4,552,076, solid fuel is delivered to the load-carrying pulverizer 20 wherein the solid fuel is ground to pulverized solid fuel and dried by hot air. The pulverized solid fuel is entrained in the pulverizer 20 in the hot air passing therethrough to dry the solid fuel and is drawn from the pulverizer 20 by exhauster 22 and conveyed through the main fuel pipes 24 to the load-carrying burners 18 for combustion in the fossil furnace 10.
With further reference to the teachings of the prior art, there is disclosed in U.S. Pat. No. 2,250,844 entitled "Centrifugal Fan", which issued on Jul. 29, 1941 and which was assigned to the same assignee as the present patent application, an exhauster of the type designed to be employed in a solid fuel pulverizer firing system. In accordance with the teachings of U.S. Pat. No. 2,250,844, solid fuel, which is delivered to the bowl 4 of the pulverizer 1, is thrown centrifugally against a grinding ring 8, crushed under rollers 9 and spills over the top edge of the grinding ring 8. Thence it is carried by an air current flowing upward around the grinding ring 8 through space 14 into a classifier 17. The coarse material travels downwardly through the bottom 18 of the classifier 17 back into the interior of the pulverizer 1, while the fine material passes upwardly in a current of air into a conduit 21 leading to an exhauster 22. The material after passing through the intake of the exhauster 22 into the interior thereof passes across the blades 20 thereof. The mixture of pulverized solid fuel and air is then delivered by the exhauster 22 through a conduit 23 to the place of use, i.e., a fossil furnace (not shown).
Although solid fuel pulverizer firing systems constructed in accordance with the teachings of the three issued U.S. patents to which reference has been made heretofore have been demonstrated to be operative for the purpose for which they have been designed, there has nevertheless been evidenced in the prior art a need for such solid fuel pulverizer firing systems to be further improved, and more specifically, a need for the exhauster employed therein to be improved. Exhausters constructed in accordance with the present day designs commonly have operating efficiencies that are on the order of 55%. A limiting factor insofar as the operating efficiency of exhausters is concerned has heretofore been the need to facilitate maintenance particularly on the rotor portion thereof. The need for such maintenance is occasioned principally by the fact that the material which is transported through the exhauster is extremely abrasive. To this end, a need has thus been evidenced in the prior art for a new and improved solid fuel pulverizer firing system, and more specifically for a new and improved exhauster for such solid fuel pulverizer firing systems that would be capable of operating at efficiencies of up to 70%.
Moreover, there has been evidenced in the prior art a need for such a new and improved exhauster for such solid fuel pulverizer firing systems that would further be characterized in a number of additional respects. One such additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is the capability to vary the position in which the blades are mounted therewithin. Another such additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is the capability, by virtue of varying the position in which the blades are mounted therewithin, of attaining optimum airflow therewith. A third such additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is the capability of realizing therewith such optimum airflow with little or no increase in power consumption. A fourth such additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is the capability, by virtue of varying the position in which the blades are mounted therewithin, of reducing therewith the amount of erosion to which the interior surfaces of the exhauster are subjected. A fifth such additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is the capability of achieving therewith an even greater reduction in the amount of erosion to which the interior surfaces of the exhauster are subjected by applying a coating of high abrasion resistant material to such surfaces. A sixth such additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is the capability of realizing therewith a reduction in the amount of leakage of airflow therefrom as contrasted to that from which prior art forms of exhausters are known to suffer. A seventh such additional characteristic which such a new and improved exhauster for such solid fuel pulverizer firing systems would desirably possess is that the exhauster would be capable of embodying all of the above-enumerated characteristics while yet retaining the existing casing of an exhauster.
It is, therefore, an object of the present invention to provide a new and improved exhauster for use in solid fuel pulverizer firing systems.
It is a further object of the present invention to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized by its high efficiency as compared to that which has been attainable heretofore with prior art forms of exhausters.
It is another object of the present invention to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that it is possible therewith to vary the position in which the blades thereof are mounted therewithin.
It is still another object of the present invention to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that by varying the position in which the blades thereof are mounted therewithin it is possible to attain therewith optimum airflow.
Another object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that it is possible therewith to realize such optimum airflow with little or no increase in power consumption.
A still another object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that by varying the position in which the blades thereof are mounted therewithin it is possible to reduce therewith the amount of erosion to which the interior surfaces of the exhauster are subjected.
A further object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems wherein it is possible to achieve therewith an even greater reduction in the amount of erosion to which the interior surfaces of the exhauster are subjected by applying a coating of high abrasion resistant material to such surfaces.
A still further object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems wherein it is possible to realize therewith a reduction in the amount of leakage of airflow therefrom as contrasted to that from which prior an forms of exhausters are known to suffer.
Yet an object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that it is possible therewith to achieve all of the foregoing within the existing casing of an exhauster.
Yet a further object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that use may be made thereof either in retrofit applications or in new applications.
Yet another object of the present invention is to provide such a new and improved exhauster for solid fuel pulverizer firing systems which is characterized in that it is relatively simple in construction, relatively easy to operate, yet is relatively inexpensive to provide.